Thermostats have long been used to control heating, ventilation, and air conditioned systems which are referred to as HVACs. More recently thermostats have been devised that may be remotely controlled by radio or infrared signals. They offer a number of advantages over those which are manually controlled as with a keypad due to the prevalence today of wireless communications such as those via the internet.
For example, remote controllable thermostats may be used to shut off a building air condition system should one have forgotten to do so before leaving. One can instruct the thermostat to postpone cooling or heating of ones home because of one's anticipated tardiness. They can also be used to monitor a building's temperature in case the air conditioner should fails or another occupant should change its program. Though radio communications with the thermostat may be established by several means, as previously stated, a popular method today is to control it via the internet through the use of an RF communications protocols such as WiFi. Representative prior art patent disclosures of this technology include U.S. Pat. Nos. 6,394,359, 7,571,865 and 8,276,829, amongst others. A problem with such wireless communications is that they require more power to operate the thermostat, thus greatly reducing the life of the battery. As such, not only does the hardware need to be as low power as possible in order to conserve the battery life, but the radio communications must be optimized in order to reduce unnecessary radio traffic. In particular, the radio should transmit at a minimal level and the radio receive time must also be at a minimal level.
Thermostats can be powered by dc batteries or by ac line power via in-place field wiring. Even so, on-board battery power is highly desirable as connections with the HVAC are often not in place in the field wiring. This in turn mandates that they operate in a low power mode to conserve battery energy. The integrated circuit (IC) devices, the display units, and the HVAC mode control logic are thus usually designed to operate under 200 uA so that they may be powered by inexpensive, small alkaline batteries with a life time of up to a year as opposed to larger capacity and more costly lithium ion batteries.
In many situations the thermostat is powered from both an onboard dc power source and/or an ac power source, namely by direct municipal line power or off the HVAC system. Even where ac power is available it is important for the unit itself to have standby dc power available as backup in the event of an ac power outage from the local power company or from a circuit breaker having been tripped. In such event it is desirable to have all batteries disconnected when the unit is operating on ac power to avoid battery discharge.
Another battery drainage source has been that of mode switch monitoring. More advanced and expensive dry contact switches have a low on resistance of the switch which requires a minimum wetting current.
It thus is seen that numerous requirements of sophisticated or smart, modern day, remote control thermostats place direct power drains on onboard battery power supplies as well as leakage during their quiescent operations. Accordingly, it is a principal object of this invention to minimize such in order to enable the onboard power source to be provided by one or more low voltage, low cost, dry cell batteries such as alkaline and yet with a substantial life span to minimize replacements. It is to the provision of such that this invention is primarily directed.